1. Field of the Invention
The invention relates generally to a method of producing a consolidated cellulosic product and more specifically to a method of producing a consolidated cellulosic product resistant to fungi.
2. Description of Related Technology
Exterior grade wood products such as millwork used for doors and windows must be treated for rot resistance to prevent deterioration from wood-destroying fungi. These wood products are usually dip-treated, vacuum-treated, or coated with a fungicide. Borates such as sodium borate are known to be effective fungicide materials for solid wood products. These treatment methods have the disadvantage of producing a "shell effect," wherein the products have rot resistance only to a very small depth from the surface of the wood product. As a result, if the wood product is cut or develops cracks or checks after the fungicide is applied, then it must be re-treated with a fungicide.
Consolidated cellulosic, e.g., wood, products include particle boards, made from wood particles, and fiberboards, made from wood fibers. Consolidated wood products are generally formed by mixing a synthetic resin adhesive or other suitable binder with wood fibers or wood particles, and then bonding together the fibers or particles in the presence of heat and pressure. When consolidated wood products, such as medium density fiberboard used to make windows or doors, are used for exterior applications, a separate step of applying fungicide is required to protect the wood product after the consolidated wood product is formed.
In the past zinc borate has been used to treat softwood wafers (a type of wood particle) that are consolidated to form waferboard (a type of particle board). Treating wood particles or fibers before a consolidated wood product is formed has the advantage of producing a product that has consistent fungus resistance throughout its cross section. Therefore, if the consolidated wood product is cut or develops cracks or checks, it maintains effective rot resistance. As known in the art, fungicides that are effective for softwood species may not be effective for hardwood species or for mixed hardwoods. Moreover, fungicides affect wood fibers differently from wood wafers or other types of wood particles. Zinc borate has never been used to treat hardwood particles or hardwood fibers to form fungus-resistant consolidated wood products.